The fire and health hazards of coating compositions in standard organic solvent form are well known. These problems have been solved in various technical areas by substitution of water as the solvent. Water soluble polyester compositions are described in Amoco Chemical Corporation Bulletin "TMA-120a/Resins WS-549/WS-5490" where water-soluble alkyd resins containing linoleic fatty acid, soya oil, trimethylolpropane, isophthalic anhydride and trimellitic anhydride were suggested for industrial coatings on farm implements and automotive engines. Laganis, in U.S. Pat. No. 3,108,083, describes a system for metal containers which comprises tricarboxylic acid, saturated aliphatic dicarboxylic acid, saturated aliphatic dihydric alcohol, water soluble phenolic resin, water soluble melamine, urea or acetone-formaldehyde, and a combination of methyl cellulose and tall oil or ricinoleic acid.
In the area of electrical insulation, Thomas and Garland, in U.S. Pat. No. 4,130,520, provided coatings having high heat resistance and high bond strength. Thomas and Garland used an aromatic dicarboxylic acid, saturated aliphatic dicarboxylic acid, unsaturated aliphatic dicarboxylic acid, saturated aliphatic dihydric alcohol, alicyclic dihydric diol, an organic compound selected from a tris (hydroxy alkyl) isocyanurate or a trihydric alcohol, an amine neutralizing base and butyl cellosolve. These coatings were useful as insulation and provided thermal ratings of up to 200.degree. C., and 2 mil bond strengths, after cure at 150.degree. C., of 26 to 28 pounds at room temperature and 5 to 9 pounds at 100.degree. C. What was needed in the area of motor insulation, however, was a coating having even higher cured bond strengths at room and at elevated temperatures.
Laganis, in U.S. Pat. No. 4,179,420, achieved up to 55 pound bond strengths at room temperature and up to about 6 pound bond strengths at 150.degree. C. There, the polyester paint type protective composition could comprise aromatic dicarboxylic acid, saturated aliphatic dicarboxylic acid, unsaturated aliphatic dicarboxylic acid, saturated aliphatic dihydric alcohol, and trihydric alcohol. This was modified with saturated or unsaturated fatty acids, tall oil and similar type oils, and melamine-formaldehyde resins.
Laganis, in U.S. Pat. No. 4,196,109 provided impregnating, electrical insulation varnishes having improved moisture resistance and extremely high bond strengths. There, the polyester was essentially the same as in the U.S. Pat. No. 4,179,420 patent, and could contain saturated aliphatic dicarboxylic acids and saturated aliphatic dihydric alcohols, but specific water soluble ortho or para substituted monoalkylphenol-phenolic hydroxy-hydrobenzoic acid mixtures were included. These particular phenolics, at 50% concentration, provided bond strengths of up to 52 pounds at room temperature and up to 17.8 pounds at 150.degree. C. Laganis, in this patent, described traditional, unmodified water-soluble phenol-formaldehyde resins as being incompatible with water-soluble alkyl systems after baking to cure; cloudy, hazy or striated cured films being formed. The complicated phenolic resins used by Laganis would add to materials and blending costs.
The search continues for even more sophisticated water dispersible polyester resin solutions which can be used, specifically as insulation for motors operating at high temperatures, where compatible, cured thin films are required, and where 150.degree. C. bond strengths of between 23 and 30 pounds, and shelf lives at least about three months are highly desirable.